when someone suddenly disappears so quickly that no one notices and everyone is so confused as to where or how that person left without any hint of them leaving. they've gotten so far away in such a short span of time its simply impossible for you not to have noticed and you wonder if secretly thye are ninjas.

you're talking to your friends and suddenly you look away and look back......there were seven of you three seconds ago....now where'd he go? your friend is ninja clouding on you